1. Field of the Invention
The invention is related to a boot comprising a sole made of at least two layered portions, i.e., a wear layer and an insert, or nerve layer, and is related to a structure of the nerve layer which is capable of providing a differentiated flexibility between the periphery of the sole and its central zone so as to encourage bending while walking, and also ensuring a good edge setting.
2. Description of Background and Relevant Information
Boots of the aforementioned type are known, in particular in Swiss Patent No. 246,465, French Patent No. 1,221,716, and U.S. Pat. No. 5,025,573.
These patents disclose soles which comprise an intermediate nerve layer provided, on the one hand, with transverse volume reductions adapted to facilitate bending of the soles while walking and, on the other hand, a relatively rigid frame delineating its periphery and allowing for edge settings or, in other words, lateral gripping.
More specifically, in the example of Swiss Patent No. 246,465 and French Patent No. 1,221,716, the nerve layer is made longitudinally flexible due to recesses that define, inside its frame, rectilinear transverse spacers, parallel with respect to one another and/or, partially in an "X", especially in the zone corresponding to the instep, i.e., near the metatarsophalangian joint of the user's foot. As is apparent, these spacers are not provided to have the ability to bend inside the frame of the nerve layer.
Indeed, French Patent No. 1,221,716 teaches that the object of the "X" shaped arrangement of the spacers is to provide a portion with a very substantial rigidity, and that the parallel arrangement of the other spacers is adapted to allow flexibility of the nerve layer, and thus of the sole, essentially when the foot is in the course of motion, i.e., about a transverse axis.
In such a construction, the nerve layer allows a very firm edge setting over sloping terrain, but has the drawback of limiting the contact surface in the sole-ground interface only along the outer edge of the sole and to a very limited extent. As a matter of fact, the transverse rigidity provided to the nerve layer by its spacers prevents the sole from being deformed in its central zone so that it can adapt to the rough spots on the ground, and it especially prevents it from curving downwardly to a significant degree in order to increase the contact surface in the sole/ground interface, and thus provide a sure and stable support that is required for propulsion.
In the example where the nerve layer of the sole comprises rectilinear transverse spacers such as described in Swiss Patent No. 246,465, such spacers are also not provided to be flexible, quite the contrary. Indeed, in each spacer, the intermediate portion located between the two ends that are affixed to the frame of the nerve layer is provided with strips of material that are folded over towards the side directed towards the wear surface of the sole, so as to increase the wear resistance of the latter.
The result of constructing spacers such as these is that when they are seen in a section, they have an open profile shaped like an inverted U, which makes them, as well as the central zone of the sole over which they extend, almost non-deformable.
At any rate, even in the absence of these folded material strips, it appears that this intermediate zone of each spacer is not capable of bending significantly with respect to the frame of the nerve layer, in a transverse direction with respect to the sole. Indeed, in the embodiment mentioned, which especially corresponds to the boot described in European Patent No. 190,714, the intermediate zone of the spacers can only bend, or more specifically curve, if it has extension characteristics, and this, in combination with the flexibility of the frame, which must again be able to become tightened so as to allow the two ends of each spacer to come together as a result of the curvature produced on the latter. However, a sole functions this way in a very random manner because its various component layers are necessarily assembled to one another and to the boot upper, especially along their peripheries, i.e., along the flame of the nerve layer, which makes it very rigid in a transverse direction. Whatever the case may be, the potential tightening of the frame of the nerve layer would also cause a tightening of the boot upper on the user's foot in the transverse direction, and this would have a substantially adverse impact on its comfort.
As has been represented schematically in the annexed FIGS. 1, 2 and 3, these known soles of the prior art, where the nerve layer 3 has rectilinear spacers 4 that are parallel to one another and oriented transversely, have proven to be ill-adapted to provide a support 5 that is sure and stable in an edge setting, especially over a sloping terrain 26, nor do they provide a good grip. As a matter of fact, the nerve layer 3 lacks the capacity to become transversely deformed inside its frame 2, thus preventing the sole, and thereby the wear layer 8 from curving downwardly in the central zone 1 under the effect of the forces that are exerted laterally along that portion of its periphery that is in contact with the ground.
Furthermore, and contrary to their lack of transverse deformation capacity, these soles are characterized by a great ability for longitudinal deformation in the direction of the course of motion of the foot due to the fact that the recesses 6 determining the spacers 4 only allow small material bridges 6' to remain at the ends thereof. Indeed, these small material bridges 6', that partially form the frame 2 of the nerve layer 3, practically constitute the only resisting means of the nerve layer 3 that are capable of resisting the longitudinal bending of the latter (FIG. 2), because the spacers are too narrow 7 to be biased in that direction in view of the largeness of the radius of curvature "R" to which the sole is subjected and the zones of weakness constituted by the material bridges 6'.
This great facility for deformation, which is advantageously preferred for certain types of boots, such as leisure, relaxation, running or walking boots, is, conversely, a hampering factor for boots adapted for hiking over hilly terrains and, generally speaking, for so-called mountaineering boots. Indeed, these boots which are used in very technical maneuvers must provide a firm and precise frontal grip that has to remain almost invariable during the course of motion of the foot, especially during the propulsion phase. In addition, these boots are adapted, even if occasionally, to be equipped with ice cleats for advancing over icy terrain and, as a result, must have a sole that is adequately rigid in the longitudinal direction so that it can be used for such a purpose.
Soles such as those described in Swiss Patent No. 246,465 and European Patent No. 190,714 have thus proven to be ill-adapted for so-called mountaineering boots because they have too much longitudinal flexibility.
This drawback also appears in the case of soles whose nerve layer is provided with a central recess in the zone corresponding to the user's instep, for example, in an embodiment disclosed by U.S. Pat. No. 5,025,573. Indeed, in this embodiment, the central recess obtained in the nerve layer leaves behind only two relatively narrow strips of material that extend into the periphery zone of the sole and in the longitudinal direction thereof. As a result, there is very little resistance to the longitudinal bending of the sole.
However, as compared to the soles described previously, this sole with a central recess in the instep zone has proven to be relatively well-adapted to provide, in the edge setting phase, a relatively sure and stable support, as well as a good grip, because it is characterized by a substantial capacity for transverse deformation in its central zone, inside the frame of the nerve layer.
However, in the absence of transverse spacers, the rough spots on the ground are neither filtered nor dampened between the wear surface of the sole and the user's foot. These soles whose nerve layer is devoid of transverse spacers have thus proven to be ill-adapted to be used in their present form in boots adapted for walking over varied and rough terrains.
To summarize, the previously known soles described hereinabove, whose nerve layer provides a differentiated flexibility between their peripheries and their central zones, continue to provide too much capacity for longitudinal deformation, together with, depending on their method of construction, excessive rigidity or excessive flexibility in the transverse direction.